Waste disposal from the chemical, agricultural and other industries is a serious contemporary problem. In particular, there are many chemical wastes such as various halogenated hydrocarbons which are not biodegradable, and thus must either be stored in secure, specialized areas or incinerated in specially-designed reactors.
For example, incineration systems have been designed for the destruction of halogenated hydrocarbons, and particularly to enable the detoxification of polychlorinated biphenyl (PCB) compounds, the manufacture of which has been discontinued in the United States since 1976 due to their persistence and ecological damage. However, large amounts of such compounds remain in storage, and are thus regarded as a significant hazard.
In one particular process, organic wastes are vaporized and completely or partially oxidized at about 1,000.degree. C. Incombustible ash is discharged directly from the reaction chamber, while off-gases are passed through a secondary combustion chamber at about 1,200.degree. C. whereby the thermal decomposition of the compound is completed. However, this incineration system not only requires two combustion chambers, each of which required a substantial input of energy, but also often fails to totally eliminate the presence of halogenated hydrocarbons in the effluent stream. It appears that this and other previous incineration systems, which provide for the combustion of halogenated hydrocarbons in the presence of air, form free chlorine gas in the combustion chamber which then reforms halogenated hydrocarbons in the exit stream. Even though the initial hazardous compound may have been degraded by these reactions, any halogenated hydrocarbon is dangerous and products such as chlorinated hydrocarbons which form within the combustion chambers due to the presence of free chlorine gas still present an impediment to the safe disposal of incineration products. Thus, if the ash formed is not clean, it must be reprocessed and retested, and the "dirty" ash must be properly encapsulated and stored until a safe disposal method becomes available.
The present invention provides a process for the disposal of halogen-containing organic compounds such as carbon tetrachloride, chloroform, trichloroethane, tetrachloroethylene, methylenechloride, the various freons, polychlorinated biphenyls, dioxins and others, by conversion to compounds which pose no environmental hazard.
Specifically, a method is provided for the disposal of halogen-containing organic compounds, which comprises pyrolizing the compound in a reducing atmosphere at a temperature in the range of about 825.degree.-1,125.degree. C. In particular, the described reaction temperature may be formed by the combustion of methane and oxygen, the methane being in a stoichiometric excess of that required to react with the oxygen, thus providing the reducing atmosphere.
The reducing atmosphere may be formed by mixing methane and the compound to be converted, said compound having been vaporized according to known methods, in a reaction vessel formed from a suitable refractory material. The required temperature may be provided by external heaters about the reaction vessel, or may be provided by the burning of the methane with limited amounts of oxygen within the reaction vessel. However, it should be noted that the methane must be in a stoichiometric excess of that required to react with the oxygen in accordance with the formula CH.sub.4 +20.sub.2 .fwdarw.CO.sub.2 +2H.sub.2 O. Under such conditions, the halogen-carbon bonds will be broken and the halogens will react with the hydrogen from the methane to form hydrogen chloride, and all organic compounds will be converted to mixtures of hydrogen, ethylene, acetylene and benzene with smaller amounts of carbon and higher aromatics. Due to the fact that excess oxygen is not present within the reaction vessel, dioxins and other chlorinated hydrocarbons are not produced or reformed. The hydrogen chloride can be stripped from the gas stream after suitable heat exchange with water, alkali, lime or generally basic wash, and the hydrocarbons and carbon may be used for fuel or chemical purposes.
It should be understood that the reducing atmosphere may be provided by use of reactants other than methane, e.g., hydrogen, but as methane is widely available and easier to use, the detailed description hereinafter set forth will be described with respect to methane. When hydrogen is used to provide the reducing atmosphere, the required temperature can be provided by the combustion of some of the hydrogen with oxygen in accordance with the equation 2H.sub.2 +O.sub.2 .fwdarw.2H.sub.2 O. This is analogous to the combustion of methane to provide the required temperature.